1. Field of the Invention
The present invention relates to the field of semiconductor manufacturing tools and, more specifically, to the performance of anodic coatings on etching tools.
2. Prior Art
It is well-known in the semiconductor industry to utilize protective coatings on tools and fixtures in order to extend their useful life. Anodic aluminum oxide coatings are frequently formed on fixtures used in plasma-assisted etching systems commonly employed to fabricate integrated circuits. Anodic coatings display many desirable characteristics, including: producing a range of plasma potentials suitable for controlling the degree of anisotropic versus isotropic etching; shaping stable, uniform, reproducible plasmas which result in stable, uniform and reproducible etch rates; retarding etching of an underlying metal substrate, thereby protecting against the introduction of metal species from a fixture into the etch gas chemistry where these metal species may alter the etch rate, as well as contaminating the wafer or devices formed on the wafer; slowing fixture erosion which can lead to dimensional changes that could, in turn, result in gas flow variations and/or poor seals; and forming a relatively dense, smooth, strong, temperature resistant, low vapor pressure material which typically reduces vacuum "pump-down" time and particulate generation to levels conducive to commercial wafer fabrication practices.
Although beneficial properties of anodic coatings are well known and practiced, in general, it is difficult to determine whether an as-anodized coating will perform satisfactorily during the lifetime recommended by the equipment manufacturer; fail prematurely, whereby interrupting maintenance and production schedules, as well as undesirably processing a number of wafers before the problem is discovered and corrected; or never respond in a satisfactory fashion to an etch environment during the initial fixture or tool "prove-in" period that is typically necessary to achieve useful, stable reproducible etch rates, which can ultimately impact and disrupt production.
It is appreciated that some technique for determining the deterioration or erosion rate of a given anodic coating prior to actual failure would be of considerable benefit, as well as aid in the prevention of the destruction of wafers or interruption of production cycles. It would be of a greater benefit, if prior to use a given anodic coating can be tested to determine its useful life. Such a predictive process can be implemented at an early stage (for example, as an initial acceptance test of a fixture/tool), to predict with certain accuracy the coating response, stability, longevity and usefulness of the anodic coating when used in plasma assisted etch environments.
Accordingly, it is an object of the present invention to use a dissipation factor measurement to predict the performance properties of an anodic coating.